1. Field of the Invention
The present invention relates to a plasmonic optical waveguide using plasmonic coupling between a nano-aperture and a nano-particle, and more specifically, to a plasmonic optical waveguide which can amplify light output from a nano-aperture by transmitting the light without loss through a nano-particle using plasmonic coupling.
2. Background of the Related Art
High-intensity light of a small size is needed in many fields such as an optical information storage device, a near field scanning optical microscopy (NSOM), lithography and the like. A general method used for generating the small and strong high-intensity light is refracting incident light using a lens. At this point, the minimum size of an output beam cannot be smaller than a diffraction limit Δ of light as shown in the following equation.
  Δ  =            λ              2        ⁢        n        ⁢                                  ⁢                  sin          ⁡                      (            θ            )                                =          λ              2        ⁢        NA            
In the above equation, Δ denotes a diffraction limit, λ denotes wavelength of light, n denotes a refractive index of a medium, θ denotes an incident angle, and NA denotes the number of openings.
Generally, an immersion lens may be used as a method for reducing the size of a light spot. Since the immersion lens may obtain the number of openings NA larger than one by increasing the refractive index of a medium, it may obtain a diffraction limit small than λ/2. However, although it is possible to secure an NA larger than one by using an immersion material, a resolution of a few tens of nanometers, which is needed for a microscope, a semiconductor or the like, is difficult to obtain since the refractive index is limited. Nano-opening is an outcome of a study which has been conducted to generate an output beam smaller than this. The nano-opening is a hole drilled in a metal thin film to be smaller than the wavelength of light, and if light enters the nano-opening, the path of the light is blocked by the metal thin film, and thus only the light smaller than the size of the nano-opening is transmitted. However, since the amount of the transmitted light is limited, there is a problem in that intensity of the output beam is low. To solve this problem, shapes of the nano-opening using surface plasmon resonance (SPR) are studied.
As a conventional prior technique related to the shape of a nano-opening, a nano-opening of a peculiar shape for amplifying intensity of incident light is disclosed in US Patent Publication No. 2008-0151360. However, since the conventional optical amplification technique based on the nano-opening accomplishes the optical amplification through surface plasmon resonance by using only a peculiar geometric shape of the nano-opening, there is a limit in obtaining an output light having a high optical amplification rate and a very small collected light compared with the incident light. Accordingly, it is disadvantageous in that it is difficult to obtain high-intensity and high-density output optical energy needed for the optical information storage device, the near field scanning optical microscopy (NSOM), the lithography and the like.
In addition, since the nano-opening should approach a sample (medium) at a gap of a few tens of nanometers to demonstrate performance of the nano-opening, it is disadvantageous in that the nano-opening is exposed to damage and contamination. Accordingly, it is disadvantageous in that if a dielectric layer is arranged on the bottom surface of the nano-opening, performance of the nano-opening is seriously lowered, and if the dielectric layer is not arranged, the nano-opening is highly probable to be damaged and contaminated since it is exposed to use environments as is.
Although a method of primarily amplifying light at the nano-opening and secondarily re-amplifying the light between metal nano-particles using a multi-surface plasmon resonance effect has been introduced to solve the problems, there is a problem in that since this method is sensitive to arrangement of nano-particles, light can be emitted when an error of a few nanometers occur at the gap between the particles.